1. Field of the Invention
The present disclosure relates to a secondary battery including integrated anode and cathode leads formed by allowing an anode lead and a cathode lead to be encompassed by a single lead film, and a method of manufacturing the same.
2. Description of the Related Art
In general, in accordance with the miniaturization and lightening of portable wireless devices such as video cameras, mobile phones, portable computers, digital cameras, and the like, the development of electric vehicles and high performance electric vehicles, with respect to secondary batteries used as driving power supplies, the development of small sized, lightweight secondary batteries having excellence in terms of energy density and charging and discharging characteristics have been in demand.
As such secondary batteries, for example, nickel-cadmium batteries, nickel-hydrogen batteries, nickel-zinc batteries, lithium secondary batteries, and the like may be used. For example, lithium secondary batteries have positive attributes such as relatively long lifespans and high energy density. In addition, according to a type of electrolyte, lithium secondary batteries may be classified as lithium metal batteries and lithium ion batteries using a liquid electrolyte and lithium polymer batteries using a high molecular solid electrolyte.
FIG. 1 is a perspective view of a general lithium secondary battery. With reference to FIG. 1, a lithium secondary battery includes an electrode assembly containing an anode and a cathode (not shown), an exterior pouch material 120 formed to encompass an edge surface of the electrode assembly to be sealed and containing an electrolytic liquid filling the interior, and an anode lead 130 and a cathode lead 140 respectively welded to the anode and the cathode of the electrode assembly and aligned to be parallel with respect to each other.
In this case, the anode lead 130 is formed by coating aluminum foil with a lithium composite oxide, allowing for the charging and discharging of lithium ions, and the cathode lead 140 is formed by coating nickel foil with a carbon material allowing for the absorption, attachment and detachment of lithium ions. In order to increase insulation properties and improve sealing strength at the time of sealing the exterior pouch material, lead films 150 and 160 may be attached to two electrode leads 130 and 140, respectively.
The lead films 150 and 160 are attached to both surfaces of the anode and cathode leads 130 and 140 to allow the anode and cathode leads 130 and 140 to be exposed externally for a predetermined distance, respectively, to be interposed between outer edges of an upper pouch 120 and a lower pouch 120. In this case, the exterior pouch material 120 is subjected to a heat fusion process performed along an edge of the exterior pouch material as well as a portion having the lead films 150 and 160 interposed between the outer edges, thus forming a sealing portion 180. Accordingly, in the case of the secondary battery, a gap between the outer edges of the exterior pouch material 120 may be sealed to prevent leakage of electrolyte filling the inside of the exterior pouch material 120.
On the other hand, a method of attaching the lead films 150 and 160 to both surfaces of the anode and cathode leads 130 and 140, respectively, may be performed by applying heat in a state in which two lead films are generally located on upper and lower surfaces of the anode and cathode leads to be subjected to heat fusion to attach the lead films to the upper and lower surfaces of the anode and cathode leads. In this case, when the anode and cathode leads are respectively sealed, problems in which sealing is difficult to perform in a case in which a gap between two leads is reduced and a secondary battery is unstable due to lead vibrations may occur.
Furthermore, when general lithium secondary batteries are in an abnormal operating state such as when internal short circuits occur, overcharging and high temperature exposure, and the like, during operating, high-pressure gases may be generated while internal electrolytes are decomposed. The generated high-pressure gases may transform battery cases and may shorten lifespans of batteries, and a serious problem such as ignition or explosion of batteries may occur. Thus, security problems may occur.